Ours (a Triton T90si) started to make a higher pitched noise after about 4 to 5 years of use. When I opened it up, I found that the brushes on the pump motor were very worn. This happens to all such motors eventually, although I don't know whether 4 to 5 years of moderate usage is about average for such wear.
I rang a few places to see if I could find replacement brushes, but was generally told that I'd have to buy an entirely new shower. I eventually rang the number that came with the shower, of a company that can maintain the showers, and they were able to supply me with a replacement motor which I fitted myself (simple enough task, you just have to make sure you remember to properly fit the seal where it attaches to the water supply section of the shower unit). Cost of a new shower would have been a few hundred euro, cost of the replacement motor was about 60 euro (all done over the phone, motor was posted out to me). We have had no problems since (motor fitted early last year as far as I can remember).
So, my advice would be to ring the maintenance number, assuming you received one when you bought the shower (it was on an adhesive label stuck to our shower unit when we bought it) - I don't recall the number offhand, but still have it at home. They may be able to tell you over the phone what the likely problem it. Don't rely on what the retailers and suppliers tell you as, based on my experience, they are inclined to just suggest buying a brand new shower. If it turns out that the motor needs replacing, you can do this job yourself if you are in any way "handy", otherwise it is about a 30 minute job for an electrician.
